Home -> Usenet -> comp.databases.theory -> Re: atomic

Re: atomic

From: paul c <toledobythesea_at_ooyah.ac>
Date: Fri, 02 Nov 2007 18:19:25 GMT
Message-ID: <NSJWi.168563$1y4.77273_at_pd7urf2no> 






Bob Badour wrote:


> paul c wrote:


...

>>
>> For example?




> 

> The set of known salaries for an employee.





If we mean salaries for one employee, eg., a single attribute relations 
like:



KnownSalariesForJoe





{10,000, 20,000},



how could we make sense of:



KnownSalariesForJoe





{}



?



eg., if the set of known salaries for "Joe" is empty, a dbms that 
supports RVA's can record this second relation, but couldn't we just as 
well have an empty value for it:



KnownSalariesForJoe






so I wonder: why allow the predicate to require a set in the first place?



One argument for why might be that the predicate has been agreed to by 
all users (after a million dollars was spent assiduously gathering 
requirements).  But when it comes to unnecessary requirements I don't 
care many how many users agree!



If we mean "known salaries for each employee", I think that phrase 
presumes that we can identify each employee which means that Codd's 
"normalization" method in his 1970 paper applies, which means in turn (I 
think) that we don't need RVA's for this relation, so for me the 
question of an empty RVA doesn't "need" to come up.



(I should say that I'd guess Bob B among others here might guess that 
I'm talking towards my usual recurring them, to do with RVA's and 
recursion, the possible importance of which I admit I haven't been able 
to express in concise terms.)
Received on Fri Nov 02 2007 - 19:19:25 CET












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